The present invention relates to telephone exchange distributors and more specifically to a protective cable head, the usual function of which is to enable the connection of cables coming from outside onto the members of the telephone exchange while protecting these members against overvoltages by means of fuses, miniature lightning arresters or spark gaps.
In the prior art, protective cable heads include a plurality of modular connection units bearing pairs of connection members at the rear, next to the cable or cables which have to be connected, and at the front, next to the application jumpers. These units are often designed as plates bearing all of the connection members for protection (fuses, lightning arresters), and are clamped together against a rigid support equipped with wireways at the rear and a panel carrying the screws of the spark gaps and the label holder at the front. For each plate the fuses and/or lightning arresters are generally located between springs in cups.
Experience has shown that fuses are not very reliable for the protection of cable heads, and that lightning arresters were not employed to the best of their possibilities because of their mounting with springs and cups, i.e. the medium-quality contact with the tails of the lightning arresters often results in poor current flow capacity. Further, contact components are of complicated design and mounting and the large number of different parts keeps the cost of such cable heads at a relatively high level. Finally, changing a component is often very difficult or, even impossible without dismantling the entire assembly.